Solid secondary lithium electrochemical cells are known in the art and typically consist of a lithium or lithium-based metal anode, a lithium-ion conducting solid electrolyte, and a cathode containing a lithium ion insertion electrode material. An insertion electrode material is capable as acting as a cathode by virtue of its ability to reversibly accommodate lithium ions physically inserted into its structure during discharge of the cell and subsequently removed therefrom during charging of the cell. Such insertion electrode materials (or intercalation compounds) include V.sub.2 O.sub.5, TiS.sub.2, V.sub.6 O.sub.13, LiCoO.sub.2 which have satisfactory specific energy densities of about 300-900 Wh kg.sup.-1 and mid-discharge voltages of about 2-3 volts.
Solid secondary lithium electrochemical cells using V.sub.6 O.sub.13 as the active cathode material are well studied. K. West et al., J. Power Sources, 14 (1985) 235-246, studied V.sub.6 O.sub.13 as a cathode material for lithium cells using polymeric electrolytes. They found that the lithium insertion reaction was reversible in the composition interval Li.sub.X V.sub.6 O.sub.13 [0.ltoreq.x.ltoreq.8]. The high stoichiometric energy density for the ultimate composition Li.sub.8 V.sub.6 O.sub.13, 890 W h/kg, is very favorable for battery applications. P. A. Christian et al., U.S. Pat. No. 4,228,226 suggest that lithiated vanadium oxides of the composition Li.sub.X VO.sub.2+y [0&lt;y.ltoreq.0.4] may be prepared chemically by treatment of VO.sub.2+y with n-butylithium in hexane. Christian et al. report that the unit cell parameters derived from X-ray powder diffraction data suggest that the compositions Li.sub.X V.sub.6 O.sub.13 have a structure very similar to that of the monoclinic V.sub.6 O.sub.13, i.e., VO.sub.2+y [0.1&lt;y&lt;0.2], prepared at higher temperature. The use of Li.sub.X VO.sub.2+y, chemically manufactured as aforesaid, as the positive electrode material in a cell, permits the manufacture of cells in the discharged state.
It has been reported in U.S. Pat. No. 4,228,226 that vanadium oxides with nominal compositions close to V.sub.6 O.sub.13 i.e. oxides with the nominal stoichiometry range from VO.sub.2.05 to VO.sub.2.2 are readily prepared by the thermal decomposition of ammonium vanadate, NH.sub.4 VO.sub.3, at a controlled rate in an inert atmosphere such as argon or nitrogen, at a temperature of approximately 450.degree. C. Furthermore, the heat treatment of V.sub.6 O.sub.13 prepared in this manner can alter the lithium capacity of the material when used as a cathode active material in solid secondary lithium cells. It has also been observed that the morphology of vanadium oxide solids can affect the lithium capacity of the material under the same circumstances.
D. W. Murphy et al., J. Electrochemical Soc. 128 (1981) 2053, report the synthesis of V.sub.6 O.sub.13 and V.sub.6 O.sub.13+X [0&lt;X.ltoreq.0.5]. Stoichiometric amounts of V.sub.2 O.sub.5 and vanadium metal powder were intimately mixed and heated to 600.degree. C. in an evacuated quartz tube. The vanadium-oxygen stoichiometry was verified by thermal gravimetric analysis in an oxygen atmosphere. V.sub.6 O.sub.13+X [0&lt;X.ltoreq.0.5] was produced by thermally decomposing the ammonium vanadate under an argon stream.
Vanadium oxides V.sub.3 O.sub.7, V.sub.4 O.sub.9, V.sub.6 O.sub.13 and V.sub.6 O.sub.13+X [0.16.ltoreq.X.ltoreq.0.5] have been examined by Murphy et al., ibid., as cathode materials in ambient temperature non-aqueous secondary lithium cells. According to Murphy et al., the best cathode materials are V.sub.6 O.sub.13 and a slightly oxygen-rich V.sub.6 O.sub.13+X. Only the latter cathode materials consistently exhibited substantial capacities, good rechargability, and high charge potentials; and therefore made the best candidates for use as cathode active materials in non-aqueous lithium secondary batteries. Conventional thermal decomposition techniques produce solid V.sub.6 O.sub.13 [O.ltoreq.X.ltoreq.0.5] having a surface area to weight ratio of only 10-12 m.sup.2 /g. The vanadium oxide must be further processed (e.g., grinded) to increase this ratio in fabricating the cathode.
It would be advantageous to have a method for synthesizing V.sub.6 O.sub.13+X [0.ltoreq.X.ltoreq.0.5] wherein the product has an inherently high surface to weight ratio. This would reduce the amount of grinding necessary after its formation.